Validate that every book has the core data: Title, Author, Date, ISBN, and Publisher. Validate that each book has NumPages. Validate that each book has Hardcover. A Book is minimally required to provide the Title, Author, Date, ISBN, and Publisher. Book is comprised of one Title, one Author, one Date, one ISBN, and one Publisher The Book data is extended with an indication of the number of pages. A Book is comprised of one NumPages The Book data is extended with an indication of whether it's a hardcover. A Book is comprised of one Hardcover